In the prior art, a steering column integrally formed with a swelling portion is molded of a steel pipe by plastic working, etc., and side faces of the swelling portion are formed with round holes or elongate holes for adjusting a column position, through which a fastening bolt of a clamp mechanism is inserted. With this configuration, the swelling portion having the column position adjusting round holes or elongate holes takes a closed sectional structure integral with the steering column. Accordingly, the steering column itself can be given high rigidity, and it is possible to reduce manufacturing costs (a material cost, a working cost and an assembling cost) and a weight as well (e.g., Japanese Patent Application Laid-Open Publication No. 8-276852 and Japanese Patent Application Laid-Open Publication No. 10-7003).
Note that the present applicant discloses, in preceding Japanese Patent Application No. 2001-238198, a hydroform process as a working method that a die assembly accommodates a thin-wall steel pipe, an interior of the steel pipe is filled with pressure water or oil, and the steel pipe is formed in a desired configuration by swelling the steel pipe. This method in the preceding application has advantages of enabling a compact design because of having no welding portion in the case of manufacturing a member taking a closed sectional structure by welding after press molding, exhibiting excellency of strength and rigidity, and reducing a working cost and a weight as well.
Further, in a telescopic type steering apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 8-276852, a steering column is constructed such that, at a front side end thereof with respect to a vehicle body, a hinge bracket fixed to the column is secured by a hinge pin to a vehicle body side lower bracket, and at a middle portion of the steering column a distance bracket fixed to the column is secured to the vehicle body by a fastening bolt through a vehicle-body-side tilt bracket taking substantially an L-shape as viewed from a side. These bracket members (the hinge bracket and the distance bracket) fixed to the column are manufactured separately from the steering column and fixed to the steering column by welding, caulking, (or clinching) etc. when assembled.
Moreover, in a steering apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 2000-53001 (FIG. 9), wires leading to switches of a winker, a wiper, a light, a horn, an ignition, etc. are bundled and thus accommodated in a harness in order to prevent a contact failure caused by vibrations, etc. when performing a tilt adjusting operation as well as a telescopic position adjusting operation and when traveling. This harness is fixed to the steering column via a harness fixing bracket by use of a clip, etc.
In the former case, however, the column position adjusting round or elongate hole formed in the swelling portion of the steering column is simply holed by a general type of working method, and a peripheral edge of this round or elongate hole is formed as an open end.
As a result, particularly in a telescopic structure requiring the elongate hole, a considerable degree of surface rigidity (flexural rigidity) of the periphery of the elongate hole at the swelling portion is not acquired, and a low level of the surface rigidity (flexural rigidity) of the swelling portion is a point that raises much concern.
Moreover, the peripheral edge of the elongate hole is the open end, and, because of the low surface rigidity (flexural rigidity) of the swelling portion, there is no alternative but to adopt a complicated machining method such as milling, etc. by way of a boring work method.
Still further, in the latter case, the hinge bracket, the distance bracket and the harness fixing bracket, which are fixed to the steering column, are manufactured separately from the steering column and welding, caulking (or clinching), etc. are adopted when assembled. Hence, there are increased the manufacturing costs (the material cost, the working cost and the assembling cost) and the weight of the steering column.